Splicing patterns of fibronectin mRNA from normal and osteoarthritic human articular cartilage.

Fibronectin, a large extracellular glycoprotein, mediates the interaction of cells with the extracellular matrix. Heterogeneity in the structure of fibronectin is largely due to the alternative splicing of three exons (IIIB, IIIA and V) during processing of the fibronectin primary transcript. Osteoarthritis, a degenerative disease of synovial joints, is characterized by a progressive loss of the articular cartilage eventually resulting in pain and loss of joint function. In contrast to the loss of most cartilage matrix proteins accompanying this process, osteoarthritic cartilage contains more fibronectin than disease-free cartilage. We examined the splicing patterns of fibronectin mRNA from adult human articular cartilage of normal and osteoarthritic joints by RNase protection (exon IIIA and exon IIIB) and reversed transcription-polymerase chain reaction (exon V) assays to determine whether or not the increased fibronectin content in osteoarthritic cartilage is also associated with differences in the splicing patterns of these three alternatively spliced exons. The results revealed no gross differences in splicing of these exons between the fibronectin mRNA isolated from adult human articular normal and osteoarthritic cartilage. Thus alterations in the structure of cartilage fibronectin do not appear to correlate with the increased level of fibronectin protein associated with osteoarthritis.